Process for the extraction of butadiene



Patented Oct. 3.0, 1945 David Craig, Silver Lake, Ohio, assignor time B.F. Goodrich Company, New York, N. Y., a v corporation or New York NoDrawing. Application July 28, 1941,

' Serial No. 404,206

2 Claims. (CL 202-41) This invention relates to a process for preventingthe polymerization of unsaturated compounds during their extraction fromgases or liquids by means of organic solvents and during theirsubsequent recovery i'rom said solvents.

In the separation or recovery of unsaturated hydrocarbons from mixturescontaining uch liquids are extracted organic solvents are usuallyselected which are immiscible therewith and permit the formation of twolayers. When the excompounds, it is common practice to use a solvent.

in which such constituents are soluble for the extraction of thesecompounds. For example, butadiene, styrene, isobutylene, andcyclopentadiene are-recovered from gas streams containing them byextraction with a solvent. This extraction may be performed by passingthe gas stream counter-current to a stream of the solvent medium in aconventional stripper r scrubbing tower. Other organic solvents havealso been effectively used for solvent extraction of aliphatichydrocarbons and these solvents are well known to the prior art. Theextraction may also be eiIected by means of a solvent such as methanolwhich may have a greater tendency to dissolve the impurities than thehydrocarbons.

Processes have also been developed by which hydrocarbons such asbutadiene and isobutylene having boiling points close to each other havebeen separated by distillation in the presence of a selective solventwhich is used because the difference in the boiling points of thehydrocarbon solutions is greater than the diflerence in the boilingpoints of the hydrocarbons. Among known selective solvents may bementioned those liquid organic compounds which contain at least oneelement selected from the group consisting of oxygen, nitrogen and thehalogens. More particularly, those solvents have been found useful whichpossess high di-electric constants ethyl ether), dimethylformamide, andcertainv aldehydes and ketones such' as butyraldehyd methyl ethylketone, and acetone. Various ar .matic solvents with active substitutedgroups such as nitrobenzene, chlorophenol, and phenol "arealsoeflective.

, solvents *may conventionally be utilized alone or in admixture andthe. material to be extracted maybe in liquid or vapor form. wheretraction is performed on material in the gaseous state, the process ispreferably performed by distilling the gaseous material counter-currentto the liquid solvent in a fractionating column so that the gases freedfrom the unsaturates are drawn oil at the top while the solutioncontaining them accumulates at the bottom, although a similar operationmay be performed in a simple scrubbing tower. In any case, theunsaturated materials are ordinarily recovered from the solventcontaining them either by a reduction in pressure, an increase intemperature, or both.

In a conventional solvent extraction system as described above,conditions may exist which result in or favor thepolymerization of theseunsaturated compounds with the attendant losses in yield and depositionof polymers in the apparatus. The conjugated dienes are especiallylikely Q to undergo such reactions. This condition obviously isundesirable and gives rise to numerous operating difllcultles' as wellas substantial losses in unsaturated compounds. The loss of even verysmall amounts of unsaturates through polymerization may become animportant economic factor over a long period of time. while the delayscaused by the necessity of removing the polymers formed may also be animportant cost factor. This action may take place. even at ordinarytemperatures, and if the extraction of the unsaturates is carried out atelevated temperatures, the condition is aggravated. ,The iron oxides andsulfides frequently found in stills and extraction- Another object ofthe present invention is to provide an efiective and desirable methodforthe solvent extraction of 51101811113 such as butadiene. Other objectswill be apparent from the fol-.

lowing description:

This invention is based on the discovery that l the presence of small.quantities of materials which function as polymerization inhibitors orantioxidants will'serve to prevent polymerization of the aforesaidunsaturates while they are being removed or extracted from the in whichthey are found or produced. The incorporation of the said materials inthe system may take placeprior to or during the contact of selectivesolvent with the unsaturated material. It is well known that thepolymerization ofunsaturated compounds frequently proceeds in a manner,

may be added to the. denuded oil to replenish and maintain the'antioxidant in proper'proportion. After condensation a liquid containingabout 30% of butadiene may be obtained. No substantial polymer formationcould be-noted on inspection of the equipment after operation for aperiod of weeks. The solvent was also substantially free from polymer.

An identical procedure carried out on another portion of the samestarting materialfor the sameperiod of time leaving out theantioxidant,

For example, unsaturated hydrocarbons such as butadiene may be recoveredfrom gas streams by the use of solvents such as saturated hydrocarbonoils obtained from naphthenic, aromatic,-

. paraflinic or mixed base crude oils, decahydronaphthalene (decalin) orthe other solvents well known for this purpose and referred to above.

The inhibitor may be incorporated into the system by adding to thesesolvents a polymerization inhibitor such as a phenolic or arylaminecompound of low volatility prior to or during their contact with thegases, and the extraction may then be performed in the usual way. Amongsuch compounds are well-known antioxidants such as paraphenylenediamine, phenyl-beta-naphthylamine, beta v naphthol, hydroquinone,phenylalpha-naphthylamine, and diphenyl paraphcnylene diamine. Qtherinhibitors well known to the art as inhibiting polymerization such ascopper stearate may be used. .The amounts of anti.- oxidants orinhibitor added may vary depending on the materials used and treated andon operating conditions and ordinarily need be only in minor proportionto the quantity of solvent. In

. general between about 011 and 1% of inhibitor polymer. The followingexamples illustratethe manner in which the invention may be applied.

g Example I g A petroleum distillate obtained from the products formedby vapor phase cracking of petroleum hydrocarbons and containing about8%of diolefins, principally butadiene-1,3, may 'be scrubbed in an ordinaryscrubbing tower filled with rings or similar material having a highsurface area, by feeding the said distillate upwardly through the towerin vapor form in counter-current to a stream of a chilled wash oil suchas a gas oil or a heavy liquid residuum rich in aromatic components. Thewash oil may be chilled to a suitable temperature; 1. e., about 0 C..Prior tov its introduction into the.-

tower the wash oil has had incorporated therewith a small quantity, sayabout 0.2%, of paraphenylene diamine asan antioxidant. The solvent oilis recovered at the bottom of the tower and the butadiene recoveredtherefrom by a radual distillation. 'The denuded wash oil may. be reusedfor another extraction.

If required smallamounts of fresh antioxidant resulted in appreciablepolymer formation sufflcient to require cleaning of the apparatus and adistillation purification of the solvent.

I Example II A mixture containing 50% butadiene along with a substantialproportion of isobutylene and other butenes as impurities may be fed atthe center of a sixty plate'bubble cap column and 95% acetone containingabout 0.1% hydroquinone is supplied at the top of the column inquantities ten times the weight of the feed. The liquid flowing from thebottom of the column is heated to boil out the purified butadiene and isrecirculated,

- while a portion of the butadiene vapor is returned to the bottom ofthe column to maintain the saturation of the descending solvent. The refmainder of the butadiene recovered from the solvent is condensed andremoved as the product. In this manner the butadiene is easily enrichedto 95% concentration. On inspection of the ap- .paratus, substantially.no gum or polymer formaweight of butadiene, sulfur dioxide, and methanoltion is detected. This is apparently due to-the I incorporation of theinhibitor, since a similar run under ordinary conditions without theinhibitor results in noticeable gum or polymer formation, particularlyafter continued operation.

Example III A mixture containing about equal parts by was placed,together with phenyl-beta-naphthylamine, in a kettle connected to athirty plate bubble cap column. A solvent consisting of an 0.8% solutionof phenyl-beta-naphthylamine in methanol was introduced at the top ofthe column and allowed to run counter-current to the ascending vapors. Areflux ratio varying from 10:1 at

the beginning to 15:1 at the end of the extrac- 7.

tion was employed. The" distillate was free from sulfur dioxide untilover 98%,v of the butadiene had been collected. No visiblepolymerizationoccurred in the column, although when distillations are performed inthe-absence of an antioxidant, the column must be cleaned at theend of.or during each run; Polymerization in the kettle was substantiallyreduced by the presence of the phenyl-beta-naphthylamine.

Example About-four parts by weightof this solvent were added to one partof a mixture of approximately." equal parts of butadiene andci-monooleflns ina kettle connected to a thirty. plate bubble capcolumn. The distillation was started, and an additional portion of .theselective solvent was intro-' duced at the top of the column andallowedto run counter-current to the ascending vapors. The eilluent vaporswhich were collected at the top of the column contained less than 2% ofbutadiene. As long as there'was an antioxidantpresent in the solventused as areflux, no P ymerization was observed in the column. When thesolvent was replaced by pure methyl ethyl ketone. however, a layer ofpolymer formed on the inside surfaces and caps 01' the column withinhalf an hour. v

I claim:

1. A process for separating butadiene Iroma mixture of butadiene andisobutylene while preventing the formation of polymeric material. whichcomprises distilling said mixture upward through a iractionating columndown which flows a stream 01' a solution of sulfur dioxide in acetonecontaining about 0.1 to 1% by weight of dissolvedphenyl-beta-naphthylamine, and recovering enriched butadiene from thesaid solution.

2. A process for separating butadiene from a mixture of butadiene andbutylenes while preventing the formation of polymeric material, whichcomprises distilling said mixture upward through a fractionating columndown which flows a stream or a solution of sulfur dioxide inmethyl ethylketone containing about 0.1 to 1% by weight of dissolvedphenyl-beta-naphthylamine, and recovering enriched butadiene from thesaid solu tion.

DAVID CRAIG.

